There has been known a technique for detecting and eliminating a partial image corresponding to, for example, a hole (e.g., a perforation or a punched hole) formed in a document using a hole punch from an image of the document read by an image reader.
For example, in a known image reader, of an image of a document read by a line sensor, a particular area (hereinafter, referred to as a “detection area”) is defined inside a predetermined range within a boundary corresponding to a document end. An image signal level change that occurs at a border of the image corresponding to the punched hole is detected in the detection area. Each occurrence of the level change is counted with respect to each of a main-scanning direction and a sub-scanning direction. When a ratio of one of the count with respect to the main-scanning direction and the count with respect to the sub-scanning direction to the other is a predetermined ratio or greater, it is determined that the image corresponds to a punched hole.